This invention relates to the use of a methanol oxidase (EC 1.1.3.13) enzyme to convert a lower alkyl alcohol such as methanol or ethanol to a lower alkyl aldehyde, such as formaldehyde or acetaldehyde, and hydrogen peroxide, in the presence of oxygen.
The most common industrial process for the production of formaldehyde is the catalytic oxidation of methanol in air at 300.degree.-600.degree. C. in the presence of a silver or a metal oxide catalyst. The resulting product is purified by distillation. Modern processes typically have a stoichiometric yield of about 90%. The value of the formaldehyde produced is roughly three times the value of the methanol consumed. Typical processes for the production of formaldehyde are disclosed in U.S. Pat. Nos. 2,812,309 and 2,849,492. U.S. production of formaldehyde in 1984 was approximately 5.7 billion pounds. Formaldehyde is primarily used in the preparation of polymers, including urea-formaldehyde, phenolic, and melamine polymers.
Perhaps the most common method of synthesizing acetaldehyde is the liquid phase oxidation of ethylene with a palladium chloride catalyst. Acetaldehyde can also be produced by the partial oxidation of ethanol. The value of acetaldehyde per pound is roughly 50% more than the value of ethanol. U.S. production of acetaldehyde in 1983 was roughly 560 million pounds, and worldwide production was over 2.3 billion pounds. Acetaldehyde is an important precursor in the synthesis of a number of products, including acetic acid, acetic anhydride n-butanol, and synthetic flavors.
Hydrogen peroxide (H.sub.2 O.sub.2) is commonly produced by the oxidation of an alkyl anthrahydroquinone, such as 2-ethyl anthrahydroquinone. In this process, the starting material is oxidized to the quinone, which is subsequently reduced to the starting material by hydrogen in the presence of a palladium catalyst.
In 1984, U.S. production of hydrogen peroxide was about 375 million pounds. The value of hydrogen peroxide on a molar basis is approximately seven times that of methanol Hydrogen peroxide is widely used as a bleaching and deodorizing agent for textiles and wood pulp, and as an oxidizing agent in chemical processes. It might also be used to render lignocellulosic residues (wheat straw, corncobs and cornstalks) suitable for consumption by ruminant livestock. See M. S. Kerley, et al., Science 230, 820-822 (1985).
Several microorganisms have been identified in recent years that have the ability to utilize methanol as a carbon source. One such organism is Hansenula polymorpha. The first step in the methanol utilization mechanism of this organism is the aerobic oxidation of methanol into formaldehyde and hydrogen peroxide. EQU CH.sub.3 OH+O.sub.2 .fwdarw.HCHO+H.sub.2 O.sub.2
In the in vivo system, the resulting hydrogen peroxide is rapidly decomposed by a catalase into oxygen and water.
The possibility of using methanol oxidase (EC 1.1.3.13) from Hansenula polymorpha in a commercial process for the production of formaldehyde from methanol was investigated by Baratti et al. This work is recorded in Biotechnology and Bioengineering 10, 333-348 (1978). Using Hansenula polymorpha DL-1 (Levine et al., Appl. Microbiol. 26, 982 (1973)) the authors studied the activity of the methanol oxidase enzyme in bound and unbound form in catalyzing the conversion of methanol to formaldehyde and hydrogen peroxide. Although the process was successful at very low methanol concentrations, the enzyme was substantially deactivated by methanol concentrations in excess of 100 millimoles per liter. A 100 mM concentration corresponds to an aqueous solution of 0.4 percent methanol by volume. This is below the feedstock concentration of methanol necessary for a commercially viable process.
Another potentially limiting factor related to feedstock concentration is product concentration. In a commercial process, it is important to achieve product concentrations high enough to permit economical separation and recovery of the products. Inactivation of the enzyme by hydrogen peroxide apparently limited the utility of the process disclosed by Baratti, et al.
Accordingly, an objective of the present invention is to provide a process for the enzymatic conversion of alcohol to aldehyde and hydrogen peroxide that permits the utilization of methanol concentrations well in excess of 0.5 percent by volume.
Another objective of the present invention is to provide a process for the enzymatic conversion of alcohol to aldehyde and hydrogen peroxide that permits the buildup of product concentrations in excess of 0.5 percent by volume. The pH may be adjusted with a volatile buffer such as a carbonate or bicarbonate buffer. Ammonium bicarbonate is one preferred buffer.